On Monday, Shohei Ohtani and Ronald Acuna Jr. were named Rookie of the Year in the American and National Leagues, respectively. But they were far from the only first-year players to make an impact in the big leagues in 2018.
It would be difficult to find a team in the history of the modern game who went through an entire season without needing to use its farm system. Sometimes, jobs are given to rookies on Opening Day, as was the case with Ohtani and the Angels. Other times, a player has to wait to be called up to make an impact, just like Acuna did with the Braves.
In 2018, both prospects entered the season as Rookie of the Year contenders, if not front-runners, in each league. But sometimes Rookies of the Year come on unexpectedly. With that in mind, here is a potential ROY candidate from each organization.
AL East
Blue Jays: Vladimir Guerrero Jr., 3B
There's a strong case to made that Guerrero, MLB Pipeline's No. 1 overall prospect, should have reached the Majors last season, even with the Blue Jays' struggles. But he didn't and ultimately finished with an absurd .381/.437/.636 line and 20 home runs while reaching Triple-A at age 19. His bat is 100 percent ready for the highest level, and once there, Guerrero is a candidate to run away with top rookie honors in the AL, regardless of when he arrives.

Orioles: Yusniel Diaz, OF
The Orioles' key acquisition in the deadline deal that sent Manny Machado to Hollywood, Diaz is yet to tap into his above-average raw power but has a good idea of what he's doing at the plate, as evidenced by his .285/.392/.449 slash line and 11-homer last season in Double-A. Some other internal options may get first crack in either right or left field as the Orioles rebuild, but Diaz should become an everyday guy for them before long.
Rays: Brandon Lowe, 2B
Lowe struggled initially upon reaching the Majors, going 0-for-19 following his debut on Aug. 5. After that, however, he slashed .273/.357/.527 with six homers in 37 games to finish the year with a career-high 28 home runs between Double-A, Triple-A and MLB. He also finished with 129 at-bats, leaving him two ABs short of exhausting his rookie eligibility. Like so many young Rays players, Lowe has the defensive versatility that could make him a near regular for Tampa Bay in 2019.
Red Sox: Michael Chavis, 3B
The defending World Series champions have a depleted farm system and few opportunities at the big league level. One of the better power-hitting prospects in the upper Minors, Chavis could contribute if Rafael Devers struggles again or the need for a right-handed-hitting first baseman arises.
Yankees: Justus Sheffield, LHP
The Yankees' greatest need is starting pitching, and Sheffield should crack the Opening Day rotation. His fastball, slider and changeup all can be three plus pitches, so it won't be a shock if he's New York's second-best starter after Luis Severino.

AL Central
Indians: Yu Chang, SS
Though he continues to face an uphill battle towards carving out a spot in Cleveland's infield, Chang, a member of the Tribe's 40-man roster, saw increased reps at third base during the regular season and regular time there in the Arizona Fall League, suggesting the hot corner could be his path of least resistance. He has the hitting ability and raw power to profile there, as well as the defensive versatility to handle a utility role.
Royals: Nicky Lopez, SS/2B
Lopez is blocked at the moment by Whit Merrifield and Raul Mondesi, but he's also sound in all phases of the game and has nothing left to prove in Triple-A. He should open the season in nothing less than a utility role and should claim at least semi-regular at-bats.
Tigers: Christin Stewart, OF
He's hit at least 25 homers in each of his three full seasons of pro ball and hit a pair of homers in 60 big league at-bats this past September. Stewart has improved his overall approach, drawing a lot more walks, while still hitting balls out of the park, something that should continue with a full-time gig in Detroit next season.
Twins: Stephen Gonsalves, RHP
The left-hander didn't fare well during his first taste of the big leagues in 2018, but he had a fantastic year, mostly in Triple-A, finishing second in the system in ERA and fifth in strikeouts, while keeping hitters to a combined .184 BAA. Gonsalves' upside might be limited, but he's ready to be a mid-rotation starter.
White Sox: Eloy Jimenez, OF
If anyone can challenge Blue Jays third baseman Vladimir Guerrero for the title of best offensive prospect in baseball, it's Jimenez. Ready last summer but kept in the Minors for service-time considerations, he'll be the foundation the White Sox build their lineup around.

MILB Video - Title: Watch: Jimenez crushes 12th homer for Charlotte - Url: http://www.milb.com/r/video?content_id=2446893883

AL West
Athletics: Jesus Luzardo, LHP
Luzardo nearly reached the Majors in 2018 in what was his first full pro campaign as well as his first fully healthy, unimpeded season since his Tommy John surgery in mid-2016. Altogether, the left-hander (in his age-20 season) compiled a 2.88 ERA and 1.09 WHIP with 129 strikeouts and 30 walks in 109 1/3 innings while ascending from Class A Advanced to Triple-A. The A's will be without many of the starting pitchers that were lost due to injuries last season, so expect Luzardo to receive an earnest look during spring training.
Angels: Griffin Canning, RHP
The UCLA product projected as an advanced college arm and lived up to that advanced billing, racing all the way to Triple-A in his first full season. His four-pitch mix with excellent command allowed him to miss bats all the way up the ladder and is why he is just about ready to hit the Angels' rotation.
Astros: Kyle Tucker, OF
The No. 5 overall pick in the 2015 Draft, Tucker has recorded back-to-back 20-20 seasons in the upper Minors. His Triple-A line (.332/.400/.590) is much more representative of his upside than the numbers from his big league debut (.141/.236/.203).

MILB Video - Title: Watch: Tucker crushes game-tying homer - Url: http://www.milb.com/r/video?content_id=2488574983

Mariners: Wyatt Mills, RHP
Viewed by scouts as a potential fast-riser when the Mariners took him in the third round of the 2017 Draft, Mills, 23, was just that in his first full season as he reached Double-A and followed it with an impressive turn in the Arizona Fall League. With right-handed delivery and profile that resembles Steve Cisheck's as well as comparable stuff, Mills has all the ingredients needed to become an impactful bullpen piece in 2019.
Rangers: Yohander Mendez, LHP
Mendez's prospect luster has dimmed a bit over the last two years, yet that won't prevent him from fitting in the middle of the Rangers' rotation. He still has a quality changeup but needs to refine his command and breaking ball.
NL East
Braves: Touki Tousssaint, RHP
The Braves have scores of young pitchers who could contend for Rookie of the Year honors next season. Toussaint gets the nod because of the pure stuff that helped him lead the system in ERA and strikeouts and because of how well his big league debut went, earning him a spot on the postseason roster.

Marlins: Victor Mesa, OF
While there currently are quite a few unknowns with Mesa, whom Miami signed for $5.5 million on Oct. 22, the consensus is that the 22-year-old outfielder shouldn't require all too much seasoning in the Minor Leagues after his success in Cuba's Serie Nacional. His plus defense in center field gives him a high floor in the big leagues, and any offensive contributions that surpass expectations could make him a ROY candidate.
Phillies: Ranger Suarez, LHP
Suarez made four uneven appearances with Philadelphia in 2018, reaching the big leagues before he turned 23, and he's the kind of smart left-hander who will learn and make adjustments. He's moved very quickly since starting the 2017 season in A ball and should fit nicely into the back end of the young Phillies rotation.
Nationals: Victor Robles, OF
Robles has taken second chair to teenage superstar Juan Soto in the Nationals' long-term outfield outlook with good reason. Yet, the future remains incredibly bright for the now 21-year-old center fielder, who hit .288/.348/.525 with three homers and three steals over 21 games with the Nats after a right elbow injury cost him much of the Minor League season. That Robles is the club's projected Opening Day center fielder at the moment makes him a preseason ROY favorite in the NL.

MILB Video - Title: Watch: Robles triples on four-hit night - Url: http://www.milb.com/r/video?content_id=2457109783

Mets: Peter Alonso, 1B
New Mets GM Brodie Van Wagenen has said he isn't opposed to having Alonso start the year in New York, and for good reason. All the first baseman did in 2018 is tie for the Minor League lead in homers, while leading it outright in RBIs. More power was on display in the AFL, and he has nothing left to prove in the Minors.
NL Central
Brewers: Keston Hiura, 2B
The best hitter from the 2017 Draft class raked his way up to Double-A in his first full season, ultimately hitting .293/.357/.464 with 52 extra-base hits including 13 homers, and has been equally impressive in the Arizona Fall League, seemingly leaving him on the cusp of entering the Majors in'19. His knack for squaring up the baseball with authority to all fields is a truly special trait -- one that could make him a key Brewers run producer for a long time.
Cardinals: Dakota Hudson, RHP
Aside from some command issues (18 BB in 27 1/3 IP), Hudson was effective in relief for the big league club in 2018. It's a crowded rotation in St. Louis, so a relief gig might be his best full-time entry for the time being where his extreme ground-ball rate (2.03 GO/AO in his Minor League career) would play well.
Cubs: Duane Underwood, RHP
Underwood still needs some polish but was more aggressive and consistent in 2018 than he had been in years past. With a 92-97 mph fastball and a curveball that shows flashes of becoming a plus pitch, he could contribute in the bullpen and possibly the rotation.
Pirates: Mitch Keller, RHP
The Pirates often are cautious with their young pitching prospects, but look for Keller to push them hard in 2019. After struggling upon first reaching Triple-A at age 22, the right-hander then had a 2.86 ERA in August. Room will have to be made in Pittsburgh's rotation, but Keller will be ready to jump through it once the door is opened.

MILB Video - Title: Watch: Keller records 10th K - Url: http://www.milb.com/r/video?content_id=2236382883

Reds: Nick Senzel, INF
A finger injury, not to mention a bout with vertigo, greatly shortened his 2018 season, and that likely kept the No. 2 pick in the 2016 Draft from getting called up this past season. He's played several positions and was working on the outfield at instructs this fall to make sure there's a spot for his advanced bat in the big league lineup in 2019.
NL West
D-backs: Taylor Widener, RHP
Widener has made a very successful transition from reliever to starter and has put his 2015 elbow surgery in his rear-view mirror with two successful, and healthy, seasons in 2017 and 2018. This last year was his first with the D-backs and he led the system in ERA and strikeouts, while holding Southern League hitters to a .197 batting average against.
Dodgers: Alex Verdugo, OF
One of the best pure hitters in the Minors, Verdugo also offers developing power, a strong arm and the ability to play anywhere in the outfield. The only thing holding him back from being a slam-dunk Rookie of the Year candidate is a clear opening in the crowded Dodgers lineup.
Giants: Chris Shaw, OF
The best power hitter in the Giants system, Shaw made his first big league home run a tape-measure shot: 468 feet off a Seunghwan Oh slider. As of now, he looks like the frontrunner to start in left field for San Francisco.
Padres: Luis Urias, 2B/SS
Urias reached the Majors late in August and showed that he can do a little bit of everything before a groin injury prematurely ended his season after just 12 games. Assuming he's on the Padres' Opening Day roster, the 21-year-old could have an early advantage in the ROY based his ability to hit near the top of an order and make everyday contributions on both sides of the ball.
Rockies: Brendan Rodgers, SS
With DJ LeMahieu set to depart as a free agent, the No. 3 overall pick in the 2015 Draft is ready to replace him at second base. He has more offensive potential than most middle infielders and the versatility to play anywhere in the infield that he's needed.

MILB Video - Title: Watch: Rodger hammers a solo blast - Url: http://www.milb.com/r/video?content_id=2225619883